Hypersensitivity Reactions Matching

Hypersensitivity reactions are classified into four types by Gell and Coombs, each with distinct mechanisms and examples. The correct matching identifies Type I as systemic anaphylaxis, Type II as chronic urticaria, Type III as Arthus reaction, and Type IV as tuberculin reaction, corresponding to option (C). This guide breaks down the types, examples, and why (C) is accurate while others fail.

Correct Answer

Option (C) P-4; Q-3; R-2; S-1 provides the precise match. Type I (P) involves IgE-mediated immediate responses like systemic anaphylaxis (4), a severe allergic reaction with rapid histamine release leading to shock. Type II (Q) features antibody-mediated cytotoxicity, exemplified by chronic urticaria (3), where IgG/IgM targets cause prolonged hives. Type III (R) results from immune complex deposition, as in the Arthus reaction (2), a localized vasculitis from antigen-antibody aggregates. Type IV (S) is delayed T-cell mediated, seen in the tuberculin reaction (1), a classic skin test response peaking at 48-72 hours.​

Type I: Systemic Anaphylaxis

Type I hypersensitivity occurs within minutes via IgE cross-linking on mast cells, releasing mediators like histamine. Systemic anaphylaxis fits perfectly, involving multi-organ symptoms such as hypotension, bronchospasm, and swelling from allergens like peanuts or bee stings.​

Type II: Chronic Urticaria

Type II involves IgG or IgM antibodies damaging cells via complement or phagocytosis. Chronic urticaria aligns as an example, often autoimmune with antibodies against FcεRI receptors on mast cells, causing persistent wheals unresponsive to antihistamines.​

Type III: Arthus Reaction

Type III arises from soluble immune complexes depositing in tissues, activating complement and neutrophils. The Arthus reaction is a prototypical local example after repeated antigen exposure, like tetanus toxoid, yielding edema, necrosis, and inflammation at the site.​

Type IV: Tuberculin Reaction

Type IV is cell-mediated by CD4+ or CD8+ T cells, without antibodies, manifesting 2-3 days post-exposure. The tuberculin (Mantoux) test exemplifies this, with induration from IFN-γ-recruited macrophages against Mycobacterium tuberculosis antigens.​

Why Other Options Fail

• Option (A) P-3; Q-4; R-2; S-1: Incorrectly assigns Type I to chronic urticaria (late-phase, not purely immediate) and Type II to anaphylaxis (IgE-driven, not cytotoxic).​

• Option (B) P-4; Q-3; R-1; S-2: Wrongly pairs Type III with tuberculin (T-cell, not immune complexes) and Type IV with Arthus (antibody-based).​

• Option (D) P-2; Q-3; R-4; S-1: Mismatches Type I with Arthus and Type III with anaphylaxis, ignoring mechanistic differences.​